The invention relates to a display device comprising a light modulation panel, a first polarization layer, a semi-transparent reflective layer, a first xc2xcxcex layer, a lens, a second xc2xcxcex layer and a second polarization layer.
Such a display device is used in, for example, head-mounted display devices, HMDs (head-mounted displays) and projection TVs. LCDs which are either transmissive or reflective are regularly used as light modulation panels. With a reflective LCD, the LCD is illuminated from the same side as the side from which it is viewed. With transmissive LCDs, the LCD is illuminated from a different size than that from which it is viewed. Notably for HMDs, the display device should be as thin as possible so that the HMD can be given a relatively compact form.
In such a display device, known from U.S. Pat. No. 5,801,885, the lens is provided with a semi-transparent reflective layer on the side facing the light modulation panel and on the side remote from the light modulation panel. Moreover, the first xc2xcxcex layer is situated between the semi-transparent reflective layer which is situated on a side of the lens facing the light modulation panel and on the side of the lens remote from the light modulation panel.
Moreover, the display device as described in U.S. Pat. No. 5,801,885 is provided with at least a second lens.
A light modulation beam coming from the light modulation panel and to be imaged on the eye is passed by the first semi-transparent reflective layer, reflected by the second semi-transparent reflective layer to the first semi-transparent reflective layer, subsequently also reflected by the first semi-transparent reflective layer and ultimately passed by the second semi-transparent reflective layer.
Whenever the light beam impinges upon a semi-transparent reflective layer, half of the light beam is passed or reflected in an unwanted direction. Since the light beam between the light modulation panel and the eye meets a semi-transparent reflective layer four times, only (xc2xd)4xc3x97{fraction (1/16)} light beam of the original light beam coming from the light modulation panel can reach the eye.
It is an object of the invention to provide a display device having an improved light output, which display device can be given a light weight and a thin form in a relatively simple manner.
In the display device according to the invention, this object is achieved in that the first xc2xcxcex layer is situated between the first polarization layer and the semi-transparent reflective layer, while the second polarization layer is a reflective polarization layer.
Since the second polarization layer is a reflective polarization layer, either full reflection or full passage of the light beam occurs on this surface. In the display device according to the invention, only a single semi-transparent reflective layer is necessary due to the reflective polarization layer. The first xc2xcxcex layer is to be situated between the first polarization layer and the semi-transparent reflective layer when using a reflective polarization layer.
A light beam coming from the light modulation panel passes through the first semi-transparent reflective layer, reflects on the reflective polarization layer, reflects again on the semi-transparent reflective layer and subsequently passes through the second reflective polarization layer. This means that the light beam impinges upon the semi-transparent reflective layer twice so that (xc2xd)2xc3x97xc2xc of the original light beam coming, from the light modulation panel can reach the eye. Consequently, the light output of the display device according to the invention is four times better than that of the display device known from U.S. Pat. No. 5,801,885.
An embodiment of the display device according to the invention is characterized in that the polarization layer and the xc2xcxcex layers are planar.
By giving the polarization layers and the xc2xcxcex layers a planar form, the display device according to the invention can easily be made from foils.
A further embodiment of the display device according to the invention is characterized in that a hologram is situated in front of the lens.
Color errors produced on the refracting surfaces can be corrected by means of the hologram. A larger magnification can then be obtained with the same optical resolution.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.